We report a strategy enabling ultrasensitive colorimetric detection of 17β-estradiol (E2) in water and urine samples using DNA aptamer-coated gold nanoparticles (AuNPs). Starting from an established sensor format where aggregation is triggered when target-bound aptamers dissociate from AuNP surfaces, we demonstrated that step-change improvements are easily accessible through deletion of excess flanking nucleotides from aptamer sequences. After evaluating the lowest energy two-dimensional configuration of the previously isolated E2 binding 75-mer aptamer (KD ∼25 nM), new 35-mer and 22-mer aptamers were generated with KD's of 14 and 11 nM by simply removing flanking nucleotides on either side of the inner core. The shorter aptamers were found to improve discrimination against other steroidal molecules and to improve colorimetric sensitivity for E2 detection by 25-fold compared with the 75-mer to 200 pM. In comparing the response of all sequences, we find that the excess flanking nucleotides suppress signal transduction by causing target-bound aptamers to remain adhered to AuNPs, which we confirm via surface sensitive electrochemical measurements. However, comparison between the 22-mer and 35-mer systems show that retaining a small number of excess bases is optimal. The performance advances we achieved by specifically considering the signal transduction mechanism ultimately resulted in facile detection of E2 in urine, as well as enabling environmental detection of E2 at levels approaching biological relevance.
Traces of antibiotics within domestic and industrial effluents have toxic impact on human health as well as surrounding flora and fauna. Potential increase in antibiotic resistance of microorganisms is likely to rise due to the incomplete removal of antibiotics by traditional wastewater processing, methods such as membrane filtration and biological treatment. In this study, we investigated a novel class of material termed polymer of intrinsic Microporosity (piM) that is based on amorphous microporous organic materials for the application of antibiotic removal form aqueous environments. the adsorption of four commonly used antibiotics (doxycycline, ciprofloxacin, penicillin G, and amoxicillin) was evaluated and found that at least 80% of the initial concentrations was eliminated under the optimized conditions. Langmuir and freundlich models were then employed to correlate the equilibria data; the Freundlich model fit well the data in all cases. For kinetic data, pseudo-first and second order models were examined. Pseudo-second order model fit well the kinetic data and allowed the calculation of the adsorption rate constants. thermodynamic parameters were obtained by conducting the adsorption studies at varied reaction temperatures. Surface potential, adsorption at various solution pHs, thermogravimetric analysis (TGA), Infrared spectroscopy (IR), and surface area experiments were conducted to draw possible adsorption mechanisms. The removal of antibiotics from water by PIM-1 is likely to be governed by both surface and pore-filling adsorption and could be facilitated by electrostatic interactions between the aromatic rings and charged functional groups as well as hydrogen bond formation between the adsorbent and adsorbate. Our work shows that the application of such novel microporous material could contribute to the removal of such challenging and persistent contaminants from wastewater with further optimizations of large-scale adsorption processes. Antibiotics are chemical compounds with a wide spectrum of applications in humans and veterinary medicine 1. They are used for treatment of diseases caused by various bacterial infections in addition to their wide usage in animal farming and aquaculture activity for disease prevention and growth promotion purposes 2-4. For example, the yearly consumption of antibiotics was estimated to be 162,000 tons for China 5 , 13,000 tons for United Sates 5 , and, 10,000 tons for European countries 5. Significant portions of the administered doses (30-90%) are excreted unmetabolized as active forms 6,7. These active antibiotic residues are found in the environment (surface water, ground water, and soil) as a result of runoff of domestic, agricultural, and industrial effluents 8. Some of the commonly used antibiotics were found to be persistent with long half-lives. Thus, they potentially pose adverse effects to water quality and aquatic life 9,10. Widespread use of antibiotics alters microbial ecosystems and exerts selective pressure on susceptible bacteria and lead to the surviva...
Synthetic DNA aptamer receptors could boost the prospects of carbon nanotube (CNT)-based electronic biosensors if signal transduction can be understood and engineered. Here, we report CNT aptasensors for potassium ions that clearly demonstrate aptamer-induced electrostatic gating of electronic conduction. The CNT network devices were fabricated on flexible substrates via a facile solution processing route and non-covalently functionalised with potassium binding aptamers. Monotonic increases in CNT conduction were observed in response to increasing potassium ion concentration, with a level of detection as low as 10 picomolar. The signal was shown to arise from a specific aptamer-target interaction that stabilises a G-quadruplex structure, bringing high negative charge density near the CNT channel. Electrostatic gating is established via the specificity and the sign of the current response, and by observing its suppression when higher ionic strength decreases the Debye length at the CNT-water interface. Sensitivity towards potassium and selectivity against other ions is demonstrated in both resistive mode and real time transistor mode measurements. The effective device architecture presented, along with the identification of clear response signatures, should inform the development of new electronic biosensors using the growing library of aptamer receptors.
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